The US Department of Labor tags a case once it is certified, denied, withdrawn or denied or certified-expired (they expire 6 months after approval so file your I-140 within that 6 months). Trackitt posts statistics about DOL here: http://stats.trackitt.com/
The latest update on PERM processing time as of June 1, 2015 is as follows:
Regular Processing: 7 months [adjudicating cases filed in/before November 2014]
Audited Applications: 18 months [adjudicating cases filed in/before December 2013]
Appealed applications (requests for reconsideration to the Certifying Officer): 2-3 months [adjudicating cases appealed in April 2015 (after a PERM case is denied and a request for appeal is sent to the Certifying Officer)]
“Government error” appealed applications. Uncertain, but colleagues are reporting that adjudication is taking over 3 months. Look for a response from DOL that the case is back in processing within 45 days of filing the PERM Appeal.